1. Field of the Invention
The present invention relates to a semiconductor wafer, particularly to a semiconductor wafer having a highly visible ID mark provided at an outer peripheral part thereof, which is suitable for providing consistent production control of a manufacturing process of a semiconductor device, and to a method for manufacturing the semiconductor wafer
2. Description of the Related Art
Usually, in a series of manufacturing processes of a semiconductor device, there are as many as several hundred processes where control of manufacturing conditions and the like are required. In manufacturing processes of the semiconductor device, strict manufacturing conditions need to be set in each manufacturing process. These manufacturing processes are controlled using an ID mark provided on a part of a principal side of the semiconductor wafer, including figures, characters, bar codes, etc.
The ID mark is usually made up of a number or a symbol showing the manufacture history for identifying the semiconductor wafer. Also, as the ID mark, a soft-mark engraved on a surface of the semiconductor wafer and a hard-mark engraved on a backside thereof are generally known. Both types of marks are made up of a plurality of recessed dots (holes) formed by irradiating the surface of the semiconductor wafer with a laser beam and locally removing silicon therefrom.
Namely, the ID mark is formed by a pulse laser beam irradiated continuously onto the surface of the semiconductor wafer through an optical system. The ID mark may have an engraved area of several mm×several cm under the present circumstances in order to ensure the visibility thereof for the people working in the manufacturing process. Therefore, the loss in element formation level area is large.
Also, dots are generally formed by irradiating a high-energy laser beam onto a part of the surface of the semiconductor wafer to melt and remove a spot-shaped part. In this case, silicon (particles) melted and removed are scattered around the dots to be deposited again on the surface of the semiconductor wafer. The particles inhibit the element formation, which greatly influences the quality of a semiconductor product.
The soft-mark formed on the surface of the semiconductor wafer in this way is recently in heavy usage in the semiconductor manufacturing process. If a chemical mechanical polishing process (hereinafter, referred to as “CMP process”) is performed repeatedly, the soft-mark is flattened and a recognition ratio thereof decreases. Moreover, since the hard-mark is formed on the backside of the semiconductor wafer, the operation to reverse the semiconductor wafer to detect the hard-mark is an added step. In addition, a slight unevenness is formed on the backside of the semiconductor wafer, which leads to a blurred focus for lithography.
In order to avoid the blurred focus in semiconductor lithography and impairment of the element formation levels of the semiconductor wafer, the laser beam is irradiated onto a bevel contour of an outer peripheral part of the semiconductor wafer using a mark pattern to form an image of a mark. Extremely minute dots with a protruding shape are thus formed, which are raised from the surface of the bevel contour.
However, the ID mark made up of such extremely minute protruding dots is cut off every time a polishing cloth is brought into contact with the bevel contour and gradually disappears. Accordingly, the visibility of the ID mark is extremely decreased. Furthermore, information about the wafer with the decreased visibility, ID mark is fed back to the processing condition for the next manufacturing process. This feed-back process control leads to a wrong setting of the process condition and a malfunction of a process device and causes a fatal defect in the quality of the product. Therefore, consistent production control of the manufacturing processes of the semiconductor device cannot be achieved.